Obesity is one of our nation's most serious public health problems which affects fully one-third of adult Americans. Dieting traditionally has been the principal treatment for this disorder but it has recently been attacked because of its poor long-term results and potentially adverse health effects. These concerns have left overweight Americans uncertain whether they should try to diet, follow one of the 'undieting' approaches recently offered to the public, or simply do nothing at all. The proposed research will compare the behavioral, psychological, and physical effects of highly restrictive dieting with three alternative methods of weight control. Thus, 200 premenopausal women, 30-100% overweight, will be randomly assigned to one of four conditions: 1) a highly restrictive diet based on a fixed menu; 2) an ~undieting~ approach designed to discourage caloric restriction and to increase self-acceptance; 3) a lifestyle approach that encourages small changes in eating and dietary habits; and 4) a minimal-treatment control group. We anticipate that subjects in the restrictive-dieting condition will report significantly greater disturbances in eating behavior, and in eating- and weight-related cognitions, during 20 weeks of initial treatment than will subjects in the three other conditions. The study will also compare these four conditions on changes in weight, body composition, resting metabolic rate (RMR), and weight-related health complications including hypertension and hyperlipidemia. We anticipate that subjects in the restrictive-dieting and lifestyle conditions will lose significantly more weight during the 20 weeks of treatment than will subjects in the two other conditions and, as a result, will display significantly greater improvements in body composition and health complications. They will also show the greatest short-term reductions in RMR. Subjects in the ~undieting~ and control conditions are expected to achieve minimal reductions in weight and health complications. Finally, we will compare changes among the four conditions on all of the above study variables during an additional 20 weeks of bi-weekly therapy and a 1-year follow-up. We expect at 1-year follow-up that subjects in the restrictive-dieting condition will regain the greatest amount of weight and will report the greatest disturbances in mood, eating behavior, and eating- and weight-related cognitions. Subjects in the ~undieting~ condition will continue to show significant improvements in psychological status but not in weight or physical health. Participants in the lifestyle condition will display significantly greater weight losses and improvements in physical health than subjects in the three other conditions, making this the preferred method of weight control.